There are many new competing battery and super high density capacitor technologies (ultra capacitors) emerging that promise to make electric vehicles truly viable.
See this article on ultra capacitors as an example of one of these new technologies. These articles often talk of ultra capacitors as if they are equivalent to batteries except that they can achieve ultra high charge and discharge rates.
I am skeptical with respect to the technology described in this particular article because it depends upon changing the dielectric to allow the ultra capacitor to hold a charge of several thousand volts. The problem with this is that what allows these high capacities to start with is a very high surface area electrode with a very thin layer of dielectric insulator. The thicker the dielectric, the less the capacitance and the less total surface area can fit in a given volume. But to withstand high voltages the dielectric has to be thick.
There is another aspect of ultra capacitors that make them a problematic replacement for a battery. A chemical battery maintains a relatively constant voltage across the majority of it’s discharge cycle. An ultra capacitor does not. This means that whatever circuitry feeds power from the ultra-capacitor to a load also needs to dynamically transform the voltage and I’m not really sure how that would be done.